Question: $f(x) = -2x^{2}+4$ What is the range of $f(x)$ ?
Answer: Consider the range of $-2x^{2}$ The range of $x^2$ is $\{\, y \mid y \ge 0 \,\}$ Multiplying by $-2$ flips the range to $\{\, y \mid y \le 0 \,\}$ To get $-2x^{2}+4$, we add $4$.